HVAC Duct Flow: Duct Sizing

Get fast answers for everyday duct and grille sizing checks. Size rectangular and round ducts, grilles and diffusers in one practical tool for the office or the field.

• Size rectangular and round (spiral) ducts by constant velocity or equal friction. • Check velocity, friction loss (Pa/m) and velocity pressure for any duct size. • Convert a rectangular a×b duct to its equivalent round diameter, and back. • Size 8 grille and diffuser types with velocity, pressure drop and throw. • Share one-page PDF reports and switch between SI and IP units. • Use the app offline on iPhone and iPad, in 15 languages.

Turn the airflow dial or type an exact value, choose a method, and review the results as they update live. Duct material roughness, air temperature and altitude are taken into account, and velocity warnings follow residential, office and industrial limits that you can tighten in Settings.

Designed for mechanical engineers, HVAC professionals and technical teams working in design, estimating or on site. Calculations follow ASHRAE Fundamentals (Darcy–Weisbach with the Colebrook equation). The app is completely free, with no ads and no data collection.

Download HVAC Duct Flow and make your next duct calculation easier.

Results are for guidance; the responsibility for design and installation remains with the engineer.